The disclosure pertains to geared drives commonly referred to as “gear motors”. Gear motors drive a wide range of different industrial machines, such as pumps, conveyors, rock crushers, rotary kilns, hoists, and some types of vehicles.
Many of these types of machines, such as oil well pumping units, air conditioning compressors, loaded ore conveyors, sand and gravel conveyors, loaded rotary kilns and loaded hoists require relatively high driving torque for starting and bringing up to operating speed. Typically, such machines are started and driven by electric motors acting through fixed ratio gearing and are therefore subjected to high starting loads. Hence, to handle the starting loads, such driving motors are usually sized larger than is required for steady running. It is well known that electric motors are most efficient when sized to be near full load during steady operation. Thus, the high starting loads combined with less than optimum running efficiency causes considerable waste of electric power.
Also, some of these types of machines, such as oil well pumping units, rock crushers, hoists and the like, experience widely varying torque loads during normal operation. Typically, electric motors used for driving such varying loads are the NEMA D “high-slip” type in order to withstand the load variation without overheating or having to be extremely oversized. Of course, both “high-slip” motors and oversized motors are considerably less efficient than correctly sized “low-slip” or “premium efficiency” motors.
In addition, some of these types of machines, such as oil well pumping units, gas compressors, boiler feed pumps and hoists must operate at variable output speeds to accommodate changing operating requirements. Typically, such speed changes are accomplished by electronic speed variation of the drive motor or by hydraulically varying the speed relation between the drive motor and the load. Both of these methods produce undesirable inefficiencies.
Therefore, it is an object of the invention to provide a gear motor having a suitably variable mechanical ratio for driving a wide variety of different machines at suitable speeds and/or variations of speeds in a highly efficient manner; to reduce and/or eliminate inherent motor starting loads; and to facilitate the use of premium efficiency motors instead of other, less efficient types.